Ferrites with square hysteresis loops



April 1961 E. ALBERS-SCHOENBERG 2,981,690

FERRITES WITH SQUARE HYSTERESIS LOOPS Filed June 18, 1957 BY M M q M rra/e/vzys Uniwd S ate This invention relatesto- .ferrite compositions which have square orrectangularhysteresis loops.

Square-hysteresisdoop ferrites have become known since about 1950. They are used on a very wide scale in memory systemsof electronic computers,-173also in; minor quantities for high-speed devices;whereithe iny ternal directional change of domain alignment functions in a manner comparable tothe' moving parts of a mechanical switch, 7

This application-is e continuation in part of ape;

plication Serial No. 442,534, filed July 12, 1954, which.

in turn is a continuation in part of 1.1.5. application Serial l percent. The minimum limitat on of 4 mole percent of No. 270,351, filed Februaryj, l952 (now abandoned), US. application Serial No. 253,779, filed October 30, 1951 (now abandoned). and US. application Serial No. 67,752, filedDecember 28, 1948 (now abandoned): 1

i The said us.- application Serial 7No. 4'42;534:relates. P toMgOMnOFe O ferrite'compositions which show;

square hysteresis loops. These compositions may cone: sist entirely of the componentsiMgO, MnO and Fe O the components being present tin-the following propor- 35 tions:

Mole percent 8 to 55 MgO MnO H 7 77 7 7 7 7 7. Bodiesused for memory core s are generally within a: somewhat narrower range- & follows;

' 1 v it lM l iper entr M'go w 49-, MnO 15 to FQ203 I to A s ubatantiallr thecp npcsitinn wh sk was d s l ed 5771 ep liea i 573, 79. 7 1'1?! 7 More recentlys are loop ferritesare allegedlyfound;

inother' syst'enis also such as in the lithium nickel ferrite. system (Belgium 534,271), lithiumcopperj ferrit system.

(Belgium 534,272), the nickel-mag'ri jsiurn-jzinc fe ite sys; tem (Belgium 534,276 and 535,193)". thefcop [nickel ferrite system (Belgium 534.277), the copper manganese ferrite system 1 7( Belgium? 534,279); the cobalt L manganese ferrite system (Belgium 534,757), the nickel manganese h magnesium ferritesystern (Belgium 535,200). 1 To obtain the square loop properties. the proportions of the various components are within certain, critical ranges. This invention difiers fromasaid. prior applications of 69 whichthis application .7 is continuation-impart in that the magnesium component o ft hef Mg0MnOFe O 7 system is replaced by a mixtureofat least two oxides, preferably by a mixture of three 'The drawing shows 1 a triaxi proportions areirfmolepercenti r a ea h re a 1 as MO. One feature of the invention relates to the compositionsdefinem by a certain triaxial area. This area reaches into a section of the triaxial diagram which prcviously was not considered to belong to the true square-looparea of the system (so long as this system In the triaxial diagram three sides of the area follow straight percentage lines: the 4% MO'7 line, the 25% MO line, and the 47.5%'Fe O line. The fourth side follows a curved line connecting the 4 MO, 66 MnO,

point. D

Another feature of the invention is the variety of metal oxides representing MO.. They are the oxides of magnesium, calcium,.zinc, and copper. 7

A third feature of the invention is the particular importance of a 7 minimpm am ount of magnesia of 2 mole; percent, which ,has to be present in any of the composi-. tions, while theother fMO components may be present.

in various proportions adding up to the limit of 25 mole MO means that the bodyfcontaihs 2 mole percent MgO and 2 mole percent of any or several of the other oxides. Except for the boundary line of4 mole percent MO, MgO is always a minor constituentas compared with the sum of the other MO components.

A, fourth feature of the invention is the specific way of 'firi'ng these bodies. As the examples show, a watervapor protective-gas firing at temperatures up to 2500" F., preferably in the vicinity of2400 F. may be used;

inpotherrz ea'ses more advantageous properties may be obtained, i.the77rnaterials are7 fir7e7d firstin air and subse-y' quently. .heatAreated, 7(7c7or7rected7i) in a, .wat rrvapOry F ni'osphere. Other. neutral 77 gases may be applied .like'-.

wise.

It of course is not irrelevant whichof the: MOFCOH; stituents at variance will be usedandjcombined in any particular case. Depending on the properties desired diflerent mixtures will be added for the MO component.

The Mgoltasisirwell knownnenhances the sharpness of the hysteresis-loop jcorners; .C11O7 actsas a flux, reduces the firing temperature, 7and,7.promot es the density of the body; CaO reduces th oer'cive'force without markedly reducing the Curie te ture,7 and7 ZnO increases saturation fiux density. (Iii higher ampunts the latter reduces the Curie temperature and impairs the rectangulari ty.)

lined area which includes all the compositions of-the indicated in everyff ase." In some cases the ratio of 7 remanence to saturation BgfiB qappears comparatively low-between 0L7 and GLS -becaUSe saturation was measu sdra rthe re ativelvh hmasne i ne fi st thn r l a 7 .i arre pv din tq a.Bi/ s.r owiu b l 77 rabQYQt -Q-t The invention can be described most accurately by- 7 7 r reference to the triaxial diagranfof thedrawing, how

everfsincel there are more than three constituents, one

1 (if-thetriaxiahcoordinates represents a number of'oxi "instead'rof onlyone. 'It is the-former MgO pararne which now represents severalibivalent" oxides; symbolic d 9* Fe 0; V

xample. I

thgutggf courselimiting the possibilities tolany Ycertain proportions. Saturation, remanence, coercive force, initial, permeability and maximum permeability are Mole percent L 47. i a as;

3 MO consists of:

9.6 mole percent MgO 2.6 mole percent CaO 7.8 mole percent ZnO The body is made by wet milling and mixing ofthe proper amounts of MgO (or MgCOg), CaCQr', ZriO, MnO (or MnCO and Fe O Thedried mixture is calcined at about 1700 F, reground, and dried and granulated. Pressed parts were fired, in air at 2 460 F. and subsequently refired in Water vapor at 210Q F. The main properties of ring-shaped cores are: 5

B =2500 gausses B =2 l00 gausses H =0.22 oersted =O Fmax. Loop corners are well developed.

Example 2 v The mole ratio as to the three components MO, MnO, and Fe O is the same as that of Example 1. MO consists of:

9.6 mole percent MgO 2.6 mole percent CuO' 7.8 mole percent ZnO p l Processing is the same as described before except that calcium is replaced by copper. Copper oxide or basic copper carbonate may Serve as raw material.

The properties of the fired body are:

B =2400 gausses B =l700 gausses H =0.24 oersted lLo=63 #max.

Corners are well developed. p The replacing of CaO by CuO results in a slightly widened loop.

Example 3 I i V I 'Mole'percent MnO 3 MO consists of:

' 9.6 mole percent MgO,

2.6 mole percent CaO 7.8 mole percent ZnO 9.6 mole percent MgQ 2.6 mole percent CuO 7.8 mole percent ZnO Processing is the same as describedin Exam les'exept that calcinmtis replaced'by. copper.

The properties of ring samples fired in air at 2410-F.

and refired in a water-vapor atmosphere at' 2100" Fr ate high manganese percentage; (Situated in the corner of I Exb'mp l 7 l i Mole percent 5.0 MnO 47.5 F6 9 47.5 MOfconsists of:

[Zn-role percentMg'O 1 mole percent CaO "2n1olepercentZnO Processingris the same as described in Examplesxl', 3"

and-'5'. I

Corners are very well developed. The loop sla s excellent.

1 mole percent CaO 2 mole percent ZnO I V v Processing is the same as described in Examples 1 and 3. The properties of the body. fired in air at 2460 F. and refired in water-vapor at 2100" F. are as follows:

B,.=2300 gausses B 1 700 gausses H -0.4 oersted. l v- #max.= Compared with the' previous examples this body'displays a 'fairly' low maximum permeability.

i V I Example 6 v p The mole ratio of the three components MO, M; and Fe O is the same as in' Example 5, but MO consists of: t

2 mole percent MgQ" 1 mole percent CuQ 2 mole percent ZnO I Processing is the same as" described in Examples" 1,- 3, and 5 except that calcium is replaced by copper. The properties of ring samples fired in water vapor at 2400 F.

are: a

B =2 -300 gausses B 1800 gausses H =0.6 oersted #o= #max;=

Examples 5 and 6' demonstrate the erred or an extremel the area Examples 5 and 6 do not rpresent the most favorable combination of oxides.) Example-6 shows afremarhably high maximum permeability indicatingrthe eficct or copper oxide as a fiuxing'agent.

The body represents a less favorable point beingfsituated on thev47.5 mole percent iron oxide boundary line;

Examples a Molepe rc ent Mo 1-5 M consists of:

7 mole percent MgO 2 mole percent CaO 6 mole percent ZnO Prolcessing is the same as indicated for the preceding formu ae.

The properties after a first fire at 2410 F. and a watervapor treatment at 2150 F. are measured as follows:

B =2800 gausses B =2150 gausses H =03 oersted 123 p =3600 Corners: well developed.

Example9 The mole ratio of the three components MO, MnO, and Fe o is the same as in Example 8, but MO consists of: 7.0 mole percent MgO 2.0 mole percent CuO 6.0 mole percent ZnO Processing is the same as described-in the preceding examples.

The properties after firing at 253S F. in nitrogen are represented by the following values:

B =2900 gausses B,=2230 gausses H,,=0.5 oersted n =2770 Corners: Sharp.

Bodies 8 and 9 are in the center of the area and show good overall properties.

Processing follows the pattern as outlined above.

The material may be fired either in one step or in two steps leading approximately to the same values,'which are:

B =2900 gausses =2050 gausses H =0.35 oersted In:

Corners: Well developed. To facilitate the survey of the examples, all of them are compiled in the followrn' g table:

Example M0 MgO OaO OuO ZnO CdO MnO F820;

20 s. 6 2 6 7.8 41 as 20 0.6 26 7.8 41 as 20 9.6 26 7.8 66 -12 20 9.6 2.6 7.8 as 42 6 2.0 1.0 2.0 62 as 6 2.0 1.0 2.0 62 as 5 2.0 1.0 2.0 41.6 47.6 16 1.0 20 6.0 4a 61 9.-. 16 1.0 1.0 6.0 46 a1 10 4.0 1.6 4. 6 62 as I claim: 7

1. A molded ferrite body displaying a substantially rectangular hysteresis loop consisting essentially of manganese oxide, ferric oxide and at least three additional bivalent oxides (MO) consisting of ZnO, MgO and at least one MO selected from the group consisting of CaO and CuO; 7

said manganese oxide consisting of 275-66 mol percent of the composition;

said ferric oxide consisting of 30-475 mol percent of the composition;

said ZnO consisting of at least 1 mol percent of the composition;

said MgO consisting of at least 2 mol percent of the composition and when over 2 mol percent being less than the sum of the mol percentages of the CaO, CuO and ZnO components;

said ferrite containing at least 1 mol percent of the bivalent oxide selected from the group consisting of CaO and CuO;

the total proportion of the MgO, ZnO, C and CuO components being 4-25 mol percent of the composition.

2. The ferrite as defined in claim 1 wherein said MO constituents comprise about 20 mol percent of the composition and consist of about 9.6 mol percent of MgO, about 8 mol percent of ZnO and an oxide selected from the group consisting of CaO and CuO in an amount approximately equal to 20 mol percent less the total mol percent of MgO and ZnO.

3. The ferrite as defined in claim 1 wherein said MO constituents comprise about 2 mol percent of MgO, 2 mol percent of ZnO and about 1 mol percent of an oxide selected from the group consisting of Ca() and CuO.

4. The ferrite as defined in claim 1, wherein said MO constituents comprise about 15 mol percent of the composition and consist of about 7 mol percent of MgO, 6 mol percent of ZnO and about 2 mol percent of an oxide selected from the group consisting of CaO and CuO.

5. The ferrite as defined in claim 1 wherein said MO constituents comprise about 10 mol percent of the composition and consist of about 4 mol percent MgO,l.5 mol percent CaO and 4.5 mol percent of ZnO.

References Cited in the file of this patent UNITED STATES PATENTS 1,997,193 Kato et al. Apr. 9, 1935 2,452,529 Snoek Oct. 26, 1948 2,452,530 Snoek Oct. 26, 1948 2,452,531 Snoek Oct. 26, 1948 2,535,025 Albers-Schoenberg Dec. 26, 1950 2,551,711 Snoek et al. .May 8, '1951 2,565,058 Albers-Schoenberg Aug. 21, 1951 2,565,111 Albers-Schoenberg Aug. 21, 1951 2,565,861 Leverenz et al Aug. 28, 1951 2,568,881 Albers-Schoenberg Sept. 25, 1951 2,640,813 Berge June 2, 1953 2,715,109 Albers-Schoenberg Aug. 9, 1955 OTHER REFERENCES Physic III, June 1936, pp. 463-483. New Developments in Ferromagnetic Materials by Snoek, pp. 69 and 91, pub. by Elsevier Pub. Co. Inc. (1947), N.Y.

R=\ LL UNITED STATES PATENT OFFICE QERTIFICATE 0F CORRECTION Patent No. 2,981,690 April 25 1961 Ernst Albers-Schoenberg It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as "corrected below.

In the drawing, lower right-hand portion of the figure,

for

EXAMPLE 9 81 1O EXAMPLE 8 82 9 EXAMPLE ll- 82 12 read EXAMPLE lO EXAMPLE 7 81 8 EXAMPLE 7 Signed and sealed this 7th day of November 1961. (SEAL) ttest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer I Commissioner of Patents USCOMM-DC- 

1. A MOLDEN FERRITE BODY DISPLAYING A SUBSTANTIALLY RECTANGULAR HYSTERESIS LOOP CONSISTING ESSENTIALLY OF MANGANESE OXIDE, FERRIC OXIDE AND AT LEAST THREE ADDITIONAL BIVALENT OXIDES (MO) CONSISTING OF ZNO, MGO AND AT LEAST ONE MO SELECTED FROM THE GROUP CONSISTING OF CAO AND CUO, SAID MANGANESE OXIDE CONSISTING OF 27.5-66 MOL PERCENT OF THE COMPOSITION, SAID FERRIC OXIDE CONSISTING OF 30-47.5 MOL PERCENT OF THE COMPOSITION, SAID ZNO CONSISTING OF AT LEAST 1 MOL PERCENT OF THE COMPOSITION, SAID MGO CONSISTING OF AT LEAST 2 MOL PERCENT OF THE COMPOSITION AND WHEN OVER 2 MOL PERCENT BEING LESS THAN THE SUM OF MOLE PERCENTAGES OF THE CAO, CUO AND ZNO COMPONENTS, SAID FERRITE CONTAINING AT LEAST 1 MOL PERCENT OF THE BIVALENT OXIDE SELECTED FROM THE GROUP CONSISTING OF CAO AND CUO, THE TOTAL PROPORTION OF THE MGO, ZNO, CAO AND CUO COMPONENTS BEING 4-25 MOL PERCENT OF THE COMPOSITION. 